The purpose of the proposed project is to study basic mechanisms involved in the repair of DNA, with particular emphasis on post-replication, or recombination-dependent repair. For this project we plan to use two bacterial species, Escherichia coli and Bacillus subtilis. The former has a well-characterized genetic system, and is amenable to analysis by conjugation and transduction. In addition, a wide variety of mutants has been isolated, sensitive to radiation and to mutagenic chemicals. In many cases the specific enzymatic defect has been identified. A large number of mutants has also been isolated from B. subtilis. This organism, because it is amenable to genetic transformation by purified DNA, provides an assay for the biological activity of biochemical intermediates in repair. We plan to examine diverse mutants for their repair capacities in an attempt to broaden our understanding of the genetic control of post-replication repair. BIBLIOGRAPHIC REFERENCES: Ganesan, Ann K. (1975) An enzymatic assay for pyrimidine dimers in DNA. In Molecular Mechanisms for Repair of DNA, Part A, P. C. Hanawalt and R. B. Setlow, ed., Plenum Press, New York, pp. 67-69. Ganesan, Ann K. (1975) Distribution of pyrimidine dimers during postreplication repair in UV-irradiated excision-deficient cells of Escherichia coli K12. In Molecular Mechanisms for Repair of DNA, Part A,P.C. Hanawalt and R.B. Setlow, ed., Plenum Press, New York, pp.317-320.